1. Field of the Invention
The present invention is broadly concerned with preformed synthetic resin splash bars of the type used as fill members in evaporative water cooling towers. More particularly, it is concerned with fill splash bars which are especially configured for a low cost construction while giving improved tower performance in use; in this regard, the splash bars of the invention are characterized by a dome-like shape presenting an uppermost, fore and aft extending apex section together with a pair of downwardly and outwardly diverging, apertured sidewalls each presenting, at the lowermost end thereof, a support for the body. Very importantly, the vertical height of the body, when resting on the spaced apart feet thereof, is greater than one-half of the lateral distance between the feet. Comparative testing using the splash bars of the present invention versus conventional prior bars demonstrates that improved tower performance results, while at the same time lowering the cost of the fill.
2. Description of the Prior Art
In general, evaporative water cooling towers include upper hot water distribution systems such as an apertured distribution basin or the like, with an underlying lowermost cold water collection basin. Commonly, a splash type water dispersing fill structure is disposed between the distribution system and cold water collection basin. Such fill structure typically includes a plurality of elongated, horizontally arranged splash bars supported at spaced intervals by an upright grid structure. In use, hot water delivered to the distribution system falls by gravity through the fill structure, where it is advantageously dispersed into droplet form. At the same time, cooling air currents are drawn through the fill structure, either by means of a motor driven fan or through use of the natural draft-inducing hyperbolic tower.
The fill structure is generally regarded as the single most important component of the cooling tower, because the fill promotes interactive thermal energy exchange between initially hot water and cooling air currents. As water droplets are formed in the fill region, the temperature difference between relatively warm water and the cooling air causes evaporation on the surface of the drops and cooling of the water occurs therefore at a rapid rate. However, as the surface temperatures of individual water droplets approach the wet bulb temperature of the surrounding air, the cooling process is diminished and is dependent upon the rate of heat transfer on the inside of the drop to the outside of the drop surface. As such, it is desirable to interrupt the fall of individual drops by splashing the drops on a fill bar, thus instantly exposing new water surfaces and, in some cases, subdividing drops into smaller droplets to increase the total water surface area available for exposure to the passing air.
As can be appreciated, the characteristics of any fill structure splash bar must meet several criteria to assure satisfactory operation and performance. First, the splash bar should provide consistent, predictable dispersal and breakup water droplets over a range of water loadings typically encountered in practice. Preferably, the descending droplets are uniformly broken into relatively fine droplet particles in a widely divergent pattern to facilitate enhancement of the cooling process. In this regard, while water droplet formation is essential to effective cooling, care must be taken to insure that this phenomenon does not occur to a point where a fine mist is formed; such mists can become entrained in the cooling air currents, and are thereby discharged to the surrounding atmosphere unless special steps are taken to insure mist removal. Thus, an important goal of a splash bar designer is to insure that the bars give adequate droplet formation, while not giving rise to the formation of mists.
Furthermore, splash bar structure should cause a minimum amount of air pressure drop in order to keep fan horsepower requirements as well as operating costs at relatively low levels. In this respect, the goal of uniform droplet formation can be seen as somewhat at odds with the requirement of minimizing pressure droplets across a given fill structure.
In addition, splash bars should have sufficient structural strength to span the distance between adjacent upright supporting grids, since deflection of the bars can cause water to be channeled toward the low part of the bar, thereby causing unequal water dispersal throughout the passing air stream and the formation of undesirable coalesced streams of water. This problem with bar deflection is of course more common when the bars are formed of synthetic resin material, since such bars often lose strength and stiffness when subjected to the elevated temperatures of the hot water to be cooled. Another important consideration is that of the cost of the fill bars. For example, a large hyperbolic induced-draft tower may utilize something on the order of 2,000,000 splash bars, each four feet in length. As a result, the use of bars formed of expensive metallic materials cannot usually be economically justified, even though metallic bars may provide very adequate cooling performance.
Other factors which enter into splash bar design include the ability to deal with contaminated organisms (which can clog splash bar openings), dirty incoming air, and ice buildup which may occur during down time in cold water locales.
In the past, splash bars have often been comprised of elongated, rectangular in cross-section bars of such wood species as redwood or treated Douglas fir. However, wood splash bars even normally rot resistant, can deteriorate due to chemicals in the water streams. Also, wood bars present serious fire hazards as soon as water flow is interrupted and the moisture remaining on the bars has evaporated.
It has also been known in the past to make use of a variety of splash bar configurations, wherein the bars are formed of synthetic resin material such as polyvinylchloride (PVC). For example, U.S. Pat. No. 3,389,895 to DeFlon describes a number of splash bar configurations, including an inverted V-shaped bar, a generally crescent-shaped bar, and sheet material with transverse corrugations. Also, it is known that certain splash bars are made up of tubular, hollow extrusions of PVC, wherein the top water-engaging surfaces is generally transversely semicircular and a bottom portion is deformed upwardly to present a pair of spaced apart lower surfaces.
U.S. Pat. No. 4,663,092 describes another type of extruded synthetic resin splash bar. The bar described in this patent includes a pair of arcuate in cross-section side margins, and an elongated, horizontal, flat top segment interconnecting the side margins. The centers of curvature of the side margins of this bar are coincident and lie beneath the body. In overall configuration, this splash bar is relatively flat, with the height thereof being substantially less than one-half the effective width of the bar.